[dmowziz]

At 30 MHz, the negative resistance is just -3.135.

If we have a crystal that works at 30MHz, there will not be oscillation if the ESR of the crystal is greater than 3.135.
That's the need for C57 at the emitter. It reduces the value of the negative resistance seen looking into the base and it also makes k<1 at frequencies where it is greater than 1 (with grounded emitter)


C58 at the collector is just for tuning with L22.. To prevent the crystal from operating at the lower modes. (if k<1 at 44 MHz, it will likely be less than 1 at 22 MHz)
Without C58, the crystal will operate at 22 MHz

I'll do more tests maybe tomorrow. Especially to oscillate at 300 MHz, with an emitter capacitance.

Please, can you explain the diode part?
Thanks